The flexible gas piping (FGP) system, also referred to as corrugated stainless steel tubing (CSST) and formerly Interior Gas Piping (IGP) was developed in Japan and first introduced into that market by Osaka Gas and Tokyo Gas Companies during the early 1980's. The system utilizes stainless steel corrugated tubing supplied in rolls or coils with field attachable fittings to distribute gas from a central supply point such as the meter or regulator to the various appliances within a house or building. The technology, which has likened the process of plumbing a house for gas to wiring a house for electricity, substantially reduces installation time and hence the associated higher cost of labor. The technology was brought to the United States by the Gas Research Institute who saw it as a means of making gas installations more competitive; thereby increasing the percentage of new construction plumbed for gas and increasing the overall consumption of natural gas on a national basis. The technology was enthusiastically endorsed and supported by major gas utilities who had seen the significant higher cost of installed piping as their single greatest obstacle to selling more gas. Code acceptance required more time and effort to obtain, but the product is now recognized by all national model codes and ANSI, the National Fire Protection Association/National Fuel Gas Code and is tested and recognized by the American Gas Association. This product will eventually supplant black-iron pipe which accounts for approximately 80% of all fuel gas piping today, as well as copper tube which, while enjoying many of the same advantages of FGP, is being banned from this application at an increasing rate.
There have been three types of fittings originally put into the field. The first fitting introduced into the field used a fiber gasket to make the seal and no special tools were needed to assemble this fitting. This fitting has a higher incidence of leaks than the flared metal to metal seals used by other manufacturers.
The second fitting introduced into the field used first a specialized tool to flatten the convolutions at the end of the CSST tube where the fitting was to be attached and then a second tool was used to put a single flare on the tube end. This product is now off the market due to failures in the tubing caused by work hardening of the stainless steel in the flattening and flaring process.
The third type of fitting was introduced into the field using no special tools to make a metal to metal seal by folding the convolutions of the tube back on itself creating a double flare. After a limited time in the field it was realized that this fitting design was inconsistent in making a leak tight seal. The remedy to the problem was to design an insert type flaring tool; this was used for about three years. A second redesign was conducted, upgrading the insert tool to a socket type flaring tool.
A current problem in installing certain fittings is the number of loose parts that the installer must assemble in the field. In a typical fitting, there is a body, a nut, a gasket and two split ring washers that must be assembled to couple the fitting to the corrugated tubing. This number of parts leads to several disadvantages including complicated assembly and the need to carry extra parts to compensate for lost or damaged parts.
US-A-2323912 discloses a pipe fitting having a first body with a plurality of radially positioned fingers which are contracted into a groove of a corrugated tubing using a die. The die is then removed and the first body is threaded onto an adapter. This fitting has certain disadvantages.
The closest prior-art document US-A-4250348 discloses a clamping device for cables in which a plurality of gripping fingers are positioned radially about a first body and are deflected towards a centerline of the first body by a tapered surface formed in a second body so as to firmly press the fingers against a cable.
The above-discussed and other drawbacks and deficiencies of the prior art are overcome or alleviated by a fitting in accordance with the present invention defined by claim 1. Viewed from one aspect, the present invention provides a fitting which includes a first body having a first internal conduit therethrough and a first centerline. The first body has a plurality of fingers integral with the first body. The fingers are positioned radially about a periphery of the first body and each of the fingers is separated from an adjacent finger by a space. A second body which mates with the first body has a second internal conduit therethrough and a second centerline. The second body has a finger deflection surface for contacting the fingers and directing the fingers towards the first centerline. The first body has first threads and the second body has second threads for engaging the first threads to couple the first body and the second body. The fitting is characterised by the second body including a sealing surface, each of the fingers and the sealing surface compressing the corrugated tubing.
The above-discussed and other features and advantages of the present invention will be appreciated and understood by those skilled in the art from the following detailed description and drawings of embodiments of the invention described by way of example.
Referring now to the drawings wherein like elements are numbered alike in the several FIGURES:
The illustrated fitting in accordance with the present invention is made up of a first body and a second body. FIG. 1 is an end view of a first body 100 and FIG. 2 is a side view, in partial cross-section, of the first body 100. First body 100 includes a central conduit 102 and external threads 104 for engaging threads on second body 200. Formed integral with first body 100 are a plurality of fingers 110 arranged radially about the first body 100. Adjacent fingers 110 are separated by a space 112. FIG. 3 is an enlarged, cross sectional view of a finger 110. Finger 110 includes an outside surface 114, an inside surface 116 and a front face 118. The outside diameter of threads 104 is greater than the outside diameter of fingers 110.
The finger 110 has a varying thickness from front face 118 to the base 120 where finger 110 joins the remainder of first body 100. The finger 110 is thickest at front face 118 and the thickness decreases as the inside surface 116 approaches the base 120. The inside surface 116 is at an angle α relative to outside surface 114 and relative to the centerline of first body 100. In an exemplary embodiment, α is 40 degrees. A finger stop surface 122 is provided on the inside of body 100 opposite inside surface 116. As described herein, finger 110 is bent inwards towards the centerline of body 100 during installation. The finger stop surface 122 serves to stop deflection of finger 110 beyond a certain point. The finger stop surface 122 is at angle β relative to inside surface 116. In an exemplary embodiment, β is 30 degrees.
As shown in FIG. 1, the front face 118 of each finger 110 is trapezoidal. The base of the trapezoid is located towards the outside of the body 100. When the fingers 110 are deflected inwards during installation, the base of the trapezoidal front face 118 contacts the base of the front face of an adjacent finger. This creates a continuous ring to provide a sealing surface as described herein.
FIG. 4 is an end view of a second body 200 and FIG. 5 is a side view, in partial cross-section, of the second body 200. Second body 200 includes a central conduit 202 which communicates with conduit 102 to allow gas to travel through the fitting. Second body 200 includes internal threads 204 that engage external threads 104 on first body 100. The inside surface of second body 200 includes a finger deflection surface 206 and a sealing surface 208. As shown in FIG. 6, the finger deflection surface 206 is frusto-conical and is at an angle y relative to the centerline of second body 200. In an exemplary embodiment, y is 15 degrees. The finger deflection surface 206 has a largest inner diameter greater then the outer diameter of fingers 210. The internal threads 204 have an inside diameter greater than the largest inside diameter of finger deflection surface 206. The finger deflection surface 206 contacts finger 110 and deflects the fingers 110 towards the centerline of first body 100. Sealing surface 208 is used to seal the corrugated tubing as described herein with reference to FIGS. 9-11. Sealing surface 208 is at an angle Δ relative to a normal to the centerline of the second body 200. In an exemplary embodiment, Δ is 15 degrees.
Second body 200 also includes a shoulder 212 which is formed by an area of increased diameter 210 in central conduit 202. The shoulder 212 serves as a stop to position a locating sleeve 300 (FIGS. 7 and 8) relative to second body 200. The locating sleeve is similar to that disclosed in U.S. Patent 5,799,989, the contents of which are incorporated herein by reference, and pending US application 08/905,373 (EP-A-0929769), the contents of which are incorporated herein by reference. The locating sleeve 300 is press fit into second body 200. Alternatively, the locating sleeve 300 may be formed integral with second body 200. The locating sleeve 300 is generally cylindrical, and may include a tapered section to facilitate insertion. As described herein, the locating sleeve helps to position the corrugated tubing upon installation of the fitting.
Installation of the fitting will now be described with reference to FIGS. 9-10. As shown in FIG. 9, the first body 100 and second body 200 may be partially joined by mating threads 104 with threads 204. The corrugated tubing 400 is cut in a valley and is snapped into the first body 100 so that fingers 110 are positioned in the first valley adjacent to the cut end of the tubing 400. The smallest inner diameter of the fingers 110 is less than the outer diameter of peaks on the corrugated tubing but greater than the outer diameter of the valleys of the corrugated tubing. Accordingly, when the corrugated tubing 400 is inserted in first body 100, a peak of the corrugated tubing 400 engages the fingers 110. The fingers 110 are resilient and spread outward slightly to allow the peak on the corrugated tubing to clear the fingers 110. Once the peak of the tubing 400 clears the fingers 110, the fingers 110 return to their original position and rest in a valley of the tubing. This interference between fingers 110 and the tubing 400 secures first body 100 to the tubing 400.
The outer diameter of the threads 104 and corresponding inner diameter of threads 204 provides a clearance 240 between the threads 204 and the fingers 110. This clearance allows the fingers 110 to deflect away from the centerline of the first body 100 without interference from the second body 200. This allows the first body 100 and second body 200 to be partially engaged when the corrugated tubing 400 is snapped into the first body 100. This facilitates installation in that the first body 100 is partially engaged with second body 200 providing the installer with a single component.
The second step is to create a seal by rotating the second body 200 relative to the first body 100 thereby drawing the first body 100 into second body 200. As first body 100 enters second body 200, the outside surface 114 of fingers 110 engage finger deflection surface 206. As the fingers 110 travel along finger deflection surface 206, the fingers 110 are deflected inwards toward the corrugated tubing 400. Locating sleeve 300 also enters the tubing 400 to locate the tubing 400 relative to the second body 200.
The first body 100 and second body 200 continue to be tightened until a seal is achieved as shown in FIG. 10. The fingers 110 have been deflected inwards and two layers of corrugated tubing 400 are compressed between the front face 118 of each finger 110 and the sealing surface 208. The two layers of tubing, or double flare, provides a metal-to-metal seal that prevents leakage.